Page:Popular Science Monthly Volume 21.djvu/403

stickleback, and the fishing-frog, or angler, and the salmons and the cod, and the herring, afford inviting objects of curious observation, or scientific and economical study or speculation, concerning the later results of which we have kept the readers of "The Popular Science Monthly" informed. The last fish we notice is the eel, the manner of the reproduction of which is yet a puzzle to naturalists. Dr. Günther says of it:

"Their mode of propagation is still unknown. So much only is certain, that they do not spawn in fresh water, that many full-grown individuals, but not all, descend rivers during the winter months, and that some of them, at least, must spawn in brackish water or in deep water in the sea; for in the course of the summer young individuals, from three to five inches long, ascend rivers in incredible numbers, overcoming all obstacles, ascending vertical walls or flood-gates, entering every larger or smaller tributary, and making their way even over terra firma to waters shut off from all communication with rivers. Such immigrations have long been known by the name of 'eel-fairs.' The majority of the eels which migrate to the sea appear to return to fresh water, but not in a body, but irregularly, and throughout the warmer part of the year. No naturalist has ever observed these fishes in the act of spawning, or found mature ova; and the organs of reproduction of individuals caught in fresh water are so little developed, and so much alike, that the female organ can be distinguished from the male only with the aid of a microscope."

THE DEVELOPMENT OF CITIES.

By M. BADOUREAU.

THE rectangular system of laying out streets has the advantage of extreme simplicity, and lends itself to a convenient adjustment of the interior of the houses of a city; but it is monotonous in the extreme, and makes communication between one quarter of the town and another very inconvenient; for the passenger is compelled to go along the two sides of a triangle to accomplish the distance represented by its hypotenuse. We have endeavored to solve the problem of the best way of arranging the streets of cities by mathematical calculations, but have found the task one leading to geometrical complications. We recommend the study to geometricians as an interesting one, and content ourselves here with stating the conclusions we have reached. We have examined the question in the two forms: By what law can we arrange the streets so as to lose the least possible amount of space, and still have the greatest possible length of roads; and, given a surface of which the shape and area are known, and the law of